Typically, the natural gas burners that provide energy for a glass melting furnace, are located in the walls of the furnace. The flames from the burners extend across the width or the length of the furnace, slightly above and approximately parallel to the top surface of the glass melt within the furnace. Heat energy is transferred from the burner flames to the top surface of the glass melt primarily by conduction and radiation. In a typical furnace, raw batch materials are added to the furnace by distributing the raw materials on top of the existing glass melt, creating a batch ‘blanket’ of raw materials on the top surface of the glass melt. The raw batch materials consist of dry particles, ranging in grain size from approximately 0.02 to 1.0 mm.
Adding the raw batch materials into a glass furnace in this manner presents several operational difficulties. First, the dry batch materials are poor conductors of heat due to their low heat transfer coefficients and radiation emissive factors. As a result, the blanket of raw batch materials on the surface of the melt functions as an insulating layer that decreases the amount of heat energy that is transferred from the burners to the glass melt.
Another issue is the disturbance of the dry materials by the glass burner flames. The flow of air from the flames causes turbulence that disturbs and picks up the dry materials. The dry materials become entrained in the exhaust gases that exit the furnace flue or stack, a situation referred to as ‘batch carryover’, resulting in environmental air emissions such as opacity and particulate matter emissions. A third issue caused by the blanket of dry batch materials is the loss of light chemical elements such as sodium from the glass melt due to volatilization of these light elements. The loss of batch materials due to carryover or volatilization alters the chemistry of the glass melt, resulting in a final glass chemistry that is outside of the desired chemical specification, which alters the properties of the final glass product. To avoid these problems with dry batches, glass melting furnace feedstock is typically wetted with water (0-5% by weight). Although batch wetting mitigates many of the problems discussed herein, it can cause others such as poor batch transport conditions, segregation, and additional energy consumption in the glass melting furnace to drive off the added water. The present invention and application presents a solution to the aforementioned problems.
A general object in accordance with one aspect of the disclosure is to provide a raw batch material feeder for glass furnaces that eliminates the raw batch material blanket that may be formed on the top surface of the melt when batch material is fed onto the top surface of the melt, and the problems associated with such a batch blanket.
Another object in accordance with another aspect of the disclosure is to eliminate the raw batch material blanket that reduces the amount of heat energy that is transferred from the gas burners to the glass, thereby increasing the efficiency of the furnace, by increasing the amount of heat energy that is transferred from the burner flames to the glass melt.
Another object in accordance with another aspect of the disclosure is to eliminate the loss of light chemical elements such as sodium from glass melt due to volatilization at high temperature.
A still further object in accordance with another aspect of the disclosure is to eliminate batch carryover. The present disclosure embodies a number of aspects that can be implemented separately from, or in combination with, each other.
A glass furnace in accordance with one aspect of the disclosure includes a furnace melt chamber for melting the raw batch materials and containing the glass melt and a screw conveyor for receiving glass batch raw materials and feeding the glass batch raw materials into the furnace.
A dam wall may be disposed between the screw conveyor and the melt chamber. The dam wall creates a well prior to the melt chamber. Heaters may be located in the well. The screw conveyors feed the raw batch materials into the lower portion of the well for partial melting prior to entering the melt chamber. The partially melted raw materials flow upward over the dam wall out of the well and into the furnace chamber.
In accordance with another aspect of the disclosure, a glass furnace includes a furnace chamber for melting the raw materials and containing the glass melt, a plurality of feed chutes to introduce raw batch materials into the furnace chamber below the melt level, and a plurality of heaters that receive batch material from the feed chutes to raise the temperature of the batch material before it is introduced into the melt in the furnace melt chamber. The furnace also includes a dam wall establishing a well or series of wells prior to the melt chamber. The wells may include heaters.
In accordance with a further aspect of the disclosure, a glass furnace includes a furnace chamber for containing a glass melt and including a wall, a batch feed hopper adjacent to the wall of the furnace to supply raw batch materials under gravity, and a screw conveyor proximate to a bottom of the hopper to receive the raw batch materials. The furnace also includes a dam wall at the end of the screw conveyor to create a well from which the partially melted batch material flows upward, and a heater within the well to heat the batch material before flowing into the furnace melt chamber.